Heat treating of metals



15 graphitic carbon.

Patented May 27, 1930 CARL I. LAUENSTEIN, F INDIANAPOLIS,

"UNITED STATE -PATENT OFFICE,

INDIANA, ASSIGNOR 'ro LINK-BELT cou- PANY, on CHICAGO, ILLINOIS, AgonPoRA'rIoN or ILL NOIS HEAT TREATING on METALS No Drawing.

by the hot dripping process, without 'such galvanizing causing anyappreciable change in the properties or structure of the material, andparticularly without suchfgalvanizing causing deteriorationin thequality of-the metal.

As generally understood, ordinary .mal leableized cast iron is granularin its structure, being composed mainly of grains of ferrite and smallarticles of carbon or ne step in the present method or process isdesigned to cause a combination of the carbon and the ferrite in orderto form pearlite or iron carbide.

' Other objects will appear from time to time in the specification andclaims.

The malleableized cast iron parts which are to be treated are firstcleaned by any suitable method and are thereafter heated. This heatingwill usually be done in furnaces, but

may, of course, be done'by any other means.

The Iron is raised to a temperature in the neighborhood of 1475" F. Thistemperature is given as approximating the best temperature, but avariation eitherabove or below this temperature is possible. Afterthema- -ter1al has reached the critical or carbon combining temperaturea part of the carbon is combinedwith ferrite. The length of time thatthe material being treated must-be held at this temperature varies withthe size ofv air, oil, water or other medium. In ordinary practice, nopart cular effort 1s made to cool the metal slowly and where it isquenched in oil ora'liquid, it is usually cooled rapidly. Where it isdesired to give the metal a tough 4 and wear-resisting outer coat, theheating op- Appllcati on flled lq 'ovemh'er 'i, I927. Serial No.231,789.

eration will be carried out in the presence I of a' carburizing agent. p

When the material being treated has been first heated and quenched, itis thereafter reheated to a temperature not exceeding the critical orcarbon combining temperature. The result of this second heating is tocause the martensite or troostite retained after the first heating tobreak down into pearlite or sorbite. This change will normally beeffected at a temperature range of 900 F. to 1200 F. After the firstheating, then, the metal may be heated a second time to approximately1200 F. and it is subsequently cooled or quenched. It may-thereafter begalvanized by hot dipping and since the normal temperatures of such hotgalvanizing are well below 1200 R, such subsequent galvaniz ing does notmaterially change the structure of the material and therefore hotgalvanizing malleableized cast iron which has been treated by the methodabove set out does not appreciably affect the strength of the metal anddoes not embrittle it.

I claim:

1. The process of heat treating malleableized cast iron which includesheating the iron to approximately 1475 quenching and reheating toapproximatel 1200 F.

2. The process of treating malleableized' cast iron which includes thefollowing steps': heating the metal to a temperature higher than thecarbon combining temperature,

quenching it and reheating it to a temperature below the carboncombining temperature. L

3. The process of treating malleableized 7 cast iron containing ferriteand .graphltlc carbon, which includes the following steps: heating it toa point above the carbon combining temperature and quenching it,reheating it to atemperature sufficient to cause the martensite andtroosite to break down to form sorbite or pearlite, and cooling it.

et. The process of treating malleableized cast iron containin ferriteand graphitic carbon, which inclu es the following steps; heating it toa point above the carbon combining temperature and quenching it to causethe formation of martensite and troostite, reheating it to a temperaturesuflicient to cause the martensite and troostite to break down to formsorbite or pearlite, and cooling it.

Si ed at Indianapolis, county of Marion and tate of Indiana, this 27thday of October, 1927.

CARL F. LAUENSTEIN.

